The present invention relates to electrical transmission systems and in particular to busses for data communication or power transmission among physically separated terminals.
Present day electrical communication systems often comprise a number of interrelated but physically separated subsystems. Data communication among these subsystems is generally accomplished by means of a data bus. In particular, modern avionic system designs are predicated on the use of a data bus network for data communication among the physically separated subsystems comprising flight and navigational avionic and flight controls.
In the aviation industry, two data communication bus approaches are currently in widespread use. The broadcast bus currently in use in many commercial aviation applications assigns one data bus exclusively to one data source terminal. Data emanating from that single transmitter can then be picked up by any number of receiver terminals. Since avionic systems may include forty or more remote subsystems, located along both the wings and the fuselage, the amount of wiring (and attendant installation and maintenance costs) can be extensive. To significantly reduce the required amount of bus wiring, and wiring connections, many military applications specify the use of a multiplex data bus approach. This approach is based on the use of a central bus controller terminal which has supreme authority over the bus as well as over all remote terminals. The remote terminals are coupled to a single main data bus, with access thereto determined by the bus controller (under software control). This multiplex data bus approach significantly reduces the wiring requirements of an avionic system, with an attendant decrease in weight and cost and an increase in reliability.
The multiplex data bus approach currently employs a voltage mode data bus, i.e., data is communicated in terms of voltage levels appearing on a main data bus. The use of the voltage mode requires that galvanic connections be made to the main data bus; thus, a remote terminal is coupled to the data bus by means of a splice connection. For example, U.S. Pat. No. 3,651,454 discloses a bus coupler which, on installation, drives two sharp contact prongs through the insulation of the bus and into the conductor strands, establishing an electrical connection.
While being generally practical and reliable, the voltage mode data bus does have some disadvantages, particularly in applications within the aviation industry. Aging and vibration may cause the contact properties at the remote terminal splice connections to deteriorate. Also, decoupling a remote terminal from the main data bus requires that the coupling electrical connection be neutralized. These disadvantages are of particular concern in the commercial aviation industry where remote avionic subsystems may be introduced or replaced throughout the commercial life of an airplane, and where reliability is of paramount importance.